Skin, soft tissue & bone infections

Question 1

What is cellulitis and what is it caused by?

Answer 1

Cellulitis is a skin and superficial soft tissue infection which is usually caused by Staph Aureus (commonly found on the skin)/ other Strep (will go in if there is a cut/immunosuppressed/diabetes). Bacteria commonly enter into the infectious site via an existing wound (e.g. abscess/ ulcer/skin break/bite)

• Will become red, hot and swollen

Question 2

What is this condition?

Answer 2

Cellulitis

(red, hot & swollen)

Question 3

What are the clinical features (signs & symptoms) of someone with cellulitis?

Answer 3

Signs

• High temp
• Unilateral
• Swelling
• Hot to touch
• Well demarcated (draw a line around area → measure if getting worse or better)

Symptoms

• Fever
• Pain → proportional to severity of the presentation
• Loss of function

Question 4

What are the risk factors of someone with cellulitis?

Answer 4

• Reduced sensation (e.g. Diabetic Neuropathy)
• Reduced circulation (e.g. Congestive Cardiac Failure).

Question 5

What investigations would you do to someone with cellulitis?

Answer 5

• Bedside
  
  • Observations (NEWS score - ?severity of infection).
  • Wound Swabs (then start empirical treatment)+ Cultures (ideally before antibiotics → to check if infection has got into blood stream → IV or topical or PO).
• Bloods
  
  • FBC (assess inflammatory response).
  • CRP (assess inflammatory response)
  • +/- blood cultures if unwell.
• Imaging
  
  • Consider Doppler Ultrasound Scan (to rule out DVT)
  • Consider MRI (able to see if osteomyelitis) Imaging

Question 6

What is the management of someone with cellulitis?

Answer 6

• Conservative (obs, pain relief, risk factor management)
  
  • Border Marking
    (assess treatment efficacy/infective spread).
• Medical
  
  • IV/PO Antibiotics (in severe infection).
  • Flucloxacillin usually first line.
• (+/- Surgical)
  
  • Potential for debridement if severe/spreading despite treatment.
  • Amputation → if spreading and resistant → spread into bone/+ tissue
  • OR able to just remove infected tissue

Question 7

What is the differential diagnosis of cellulitis?

Answer 7

• Necrotising fasciitis
• Chronic venous changes
• Deep vein thrombosis
  *

Question 8

What is necrotising fasciitis (causes, clinical features, diagnosis, management & investigations)?

Answer 8

What it is & what causes it?

• This is a severe soft tissue infection caused by Group A Strep (Strep Pyogenes).
• Release of toxins by S. Pyogenes exacerbates extent of tissue damage by the infection (can lead to Septic Shock/Toxic Shock Syndrome.) → Tissue necrosis at the infected site also allows dissemination of infective material into the blood stream and cause a Systemic Response.

Clinical features

• This presents with a hot, red, swollen area of skin with necrotic tissue and SEVERE PAIN (pain extends further than rash).
• Poorly demarcated edges with areas of purple/black tissue (necrosis).

DIAGNOSIS:

• Skin swabs which are sent for MC&S.

MANAGEMENT:

• Medical: Broad Spectrum IV Antibiotics, Analgesia, IV Fluid. (as LOW BP)
• Surgical debridement to prevent spread of infection (need a margin clear of infection) +/- amputation.

Investigations

• Bedside: Observations, Wound Swab.
• Bloods: FBC, U&Es, CRP, Blood Cultures (high risk of septicaemia), Lactate (tissue necrosis). Likely ABGs/VBGs.
• Imaging: USS Leg (?gas gangrene within the tissue).

Question 9

What is this condition?

Answer 9

Necrotising Fasciitis

Question 10

How could we differentiate necrotising fasciitis clinically from cellulitis?

Answer 10

• Pain is disproportionate to the area of infection in NF (pain is much wider spread than the area of visible infection).
• Areas of necrosis are seen in NF (not usually seen in cellulitis).
• Poorly demarcated edges in NF (usually relatively clear borders in cellulitis).
• Patient are usually much more unwell with necrotising fasciitis.
• HIGH NEWS score in NF

Question 11

What is chronic venous changes (common name for it, and mechanism of how it happens)

Answer 11

• Lipodermatosclerosis (inverted champagne appearance) results from chronic inflammation and fibrosis of the dermis and subcutaneous tissue of the lower legs. This is characterized by painful inflammation above the ankles, which may be mistaken for cellulitis or phlebitis. Chronic venous insufficiency leads to oedema and hemosiderin deposition (causes brown discolouration of the legs), and deposition of other waste substances → Venous insufficiency prevents waste substances and fluid flowing from the lower limbs back to the central circulatory system. It therefore leaks out into the tissues of the lower limbs and causes discolouration***, ***swelling*** and ***inflammation.

Question 12

What is this condition?

Answer 12

Chronic Venous Changes → Lipodermatosclerosis

Question 13

How could we differentiate Chronic Venous Changes (Lipodermatosclerosis)clinically fromcellulitis?

Answer 13

• Not hot to touch, usually not painful, almost always BILATERAL

Question 14

What is this condition?

Answer 14

Deep Vein Thrombosis

Question 15

What is a DVT (risk factors, relevent

Answer 15

Deep Vein Thrombosis presents with a red, swollen UNILATERAL lower limb. DVT within a blood vessel causes thrombophlebitis which causes calf tenderness. May also present with low grade pyrexia. Thrombus is usually within the Femoral/Popliteal vein.

Risk factors for DVT include: immobilisation, malignancy, pregnancy, COCP/HRT, clotting disorders, surgery.

Relevant Investigations:

Doppler Ultrasound imaging

D-Dimer → sensitive but includes INFLAMMATION & ClOT

WELL’S Score → do before D-dimer

Question 16

How could we differentiate DVT clinically from cellulitis?

Answer 16

DVT → not hot to touch, well demarcated, risk factors, history

• Lower limb would be hot to touch in cellulitis, but less likely so in DVT.
• Note: Low grade pyrexia can develop in DVT due to inflammatory response caused by blood clot.
• Also take into account the difference in clinical risk factors – a patient who presents with a discharging wound and surrounding redness most likely has cellulitis, a patient who presents with a spontaneously red and swollen leg three days after a hip replacement most likely has a DVT.

Question 17

What is this condition?

Answer 17

Osteomyelitis

Question 18

What is osteomyelitis? (common causative organisms, risk factors)

Answer 18

Osteomyelitis is an infection of the bone. Most cases are acute and bacterial in origin, however patients can develop chronic osteomyelitis (able to see on X-ray)if the infection does not fully resolve.

Common causative organisms

• S. aureus (most common), Streptococci,Enterobacter spp., H. Influnzae, P.aeruginosa (especially in intravenous drug users).

Risk factors for developing osteomyelitis:

• Diabetes Mellitus
• Immunosuppression (long term steroids/AIDS).
• Alcohol excess.
• Intravenous drug use.

Question 19

What are the clinical features of osteomyelitis?

Answer 19

• Severe, constant pain* in the affected region.
  
  • In patients with diabetic foot, pain may be absent due to peripheral neuropathy.
• Loss of function (e.g. unable to weight bear, unable to pick things up).
• On examination, the site will be tender. There may be overlying swelling and erythema.
• Pyrexia.

Question 20

What is the link between osteomyelitis and diabetic foot?

Answer 20

Question 21

What are the common sites of osteomyelitis?

Answer 21

• In adults, the vertebrae are the most commonly affected bones.
• Great Hallux is also commonly affected.

Question 22

What is the cause of osteomyelitis?

Answer 22

Osteomyelitis can be caused by haematogenous spread (bacteraemia disseminates from elsewhere via the blood stream), direct inoculation of micro-organisms into the bone (such as following an open fracture or penetrating injury), or direct spread from nearby infection (such as cellulitis).

Question 23

What is Potts disease?

Answer 23

Question 24

What are the investigations and management of osteomyelitis?

Answer 24

Investigations

Bedside - Observations (fever, ?septic), Wound swabs.

Blood test - FBC, CRP, U&Es, Blood cultures (positive in around 60% cases)

Imaging - Plain film → severe (X-rays, MRI → if acute (Definitive diagnosis).

• Gold Standard = bone biopsy at debridement → >90% sensitivity Management

Medical - Long Term IV Antibiotics (4-6 weeks).
Tailored to culture results if available

Surgical - If the patient clinically deteriorates, the limb shows evidence of deterioration, or imaging shows progressive bone destruction, then surgical management may be required to prevent chronic osteomyelitis developing.

Question 25

What are the radiographic features of osteomyelitis?

Answer 25

• osteopenia
• periosteal thickening
• endosteal scalloping
• focal cortical bone loss

Question 26

What is septic arthritis? (main causitive organisms)

Answer 26

• Is the inflammation of the joint capsule
• May need joint replacement
• Usually localised joint pain (restriction in movement)

What is septic arthritis?

Septic arthritis refers to the infection of a joint. It requires a high index of suspicion and can affect both native and prosthetic joints.

Main causative organisms?
The main causative organisms that lead to septic arthritis are S. aureus (most common in adults) and Gonorrhoea (more common in sexually active patients).

Bacteria will ‘seed’ to the joint from a bacteraemia (e.g. recent cellulitis, UTI, chest infection), a direct inoculation, or spreading from adjacent osteomyelitis.
Septic arthritis can cause irreversible articular cartilage damage leading to severe osteoarthritis so must be identified EARLY.

Question 27

What are the investigations & management of septic arthritis?

Answer 27

Investigations

Bedside -Observations (fever, ?septic), JOINT ASPIRATION (joint fluid analysis) → done before IV antibiotics given

Blood tests - FBC, CRP, Urate Level (check for gout), Coag, Blood cultures (could be seeded infection).

Imaging - plain film X-ray

Management

Medical - long term IV antibiotics (4-6 weeks) (empirical and then specific after cultures come back)

Surgical - Infected native joints require surgical irrigation and debridement (‘washout’ → to get rid of as much bacteria as possible) to aid in source control. May require several washouts before clearance of infection.

Infected prosthetic joint, washout is still required, but revision surgery is typically needed also

Question 28

What are the differential diagnosis of septic arthritis?

Answer 28

• Osteomyelitis
  See previous slides.
• Crystal Arthopathies (e.g. Gout/Pseudo Gout) (→ looks like septic arthritis )joint
  Crystal deposition within the joint space causes inflammation.
• Inflammatory Arthropathies (e.g. Rheumatoid)
  Can cause acute flares, however commonly affects more than one joint.
• Haemarthrosis (→ bleeds into joint)
  Bleeding into joint space which may be associated with clotting disorders/therapeutic anticoagulation (e.g. patient on Warfarin within a knee injury).
• Reactive Arthritis
  Localised presentation of a systemic conditions (e.g. acute arthritic flares associated with IBD).

Question 29

What are the clinical features of septic arthritis?

Answer 29

• An acutely Red, Hot, Painful Joint is Septic Arthritis until proven otherwise (or at least until Orthopaedics have been to review it).
• Single swollen joint causing severe pain (most commonly the Knee Joint).
• Pyrexia will be in around 60% of affected individuals (although its absence should not rule out septic arthritis).
• On examination, the joint will appear red, swollen, and warm, causing pain on active and passive movement (rigid joint, no movement tolerated, unable to weight bear).
• Symptoms are more florid and obvious in native joint injection. In prosthetic joint infections, the features can be more subtle.